1. Field of the Invention
This invention relates generally to apparatus for stimulating a paralyzed or non-inervated lateral rectus muscle of the eye and more particularly concerns an extraocular muscle sensor and stimulator apparatus and method.
2. Description of the Prior Art
With reference to FIGS. 1 and 2, the basic anatomy of the human eye 10 will be shown. Human eyes 10, known to those skilled in the art as "globes", are coated with tissue known as conjunctiva and Tenon's fascia 20. The cornea 30 covers the iris 40 and the pupil 50. The substance of the eyeball itself is the sclera 60. The optic nerve 70 originates at the back of the globe. The eyes 10 are moved by the extraocular muscles. Each eye has six of these extraocular muscles, the lateral rectus 80, the medial rectus 90, the superior rectus 100, the inferior rectus 110, the inferior oblique 120 and the superior oblique 130.
The extraocular muscles 80, 90, 100, 110, 120 and 130 are controlled by three of the twelve cranial nerves: the third cranial nerve, known to those skilled in the art as "CN III" or the oculomotor nerve, the fourth cranial nerve, known to those skilled in the art as "CN IV" or the trochlear nerve, and the sixth cranial nerve, known to those skilled in the art as "CN VI" or the abducens nerve.
As is well known to those skilled in the art, CN III, the oculomotor nerve, stimulates the superior rectus muscle 100, the medial rectus muscle 90, the inferior rectus muscle 120, and the inferior oblique muscle 120 (shown only in FIG. 2). The superior rectus muscle 100 is responsible for upward rotation of the eye. The medial rectus muscle 90 is responsible for in-turning the eye. The inferior rectus muscle 110 is responsible for downward rotation of the eye. The inferior oblique muscle 120 is responsible for extortional rotation of the eye.
As is also well known to those skilled in the art, CN IV, the trochlear nerve, stimulates the superior oblique muscle (known as SO). The superior oblique muscle 130 is responsible for intortional rotation of the eye. Finally, CN VI, the abducens nerve, stimulates the lateral rectus muscle 80. The lateral rectus muscle 80 is responsible for out turning of the eye.
The sixth cranial nerve often becomes paralyzed in patients during or after neurological diseases such as trauma, stroke, high blood pressure, diabetes, tumors and the like. Also, some patients are born without sixth cranial nerves in a condition known as Duane's Retraction Syndrome. Paralysis of the sixth cranial nerve often causes the sighted patient to suffer from bothersome double vision, or diplopia. Prior art solutions to diplopia involve treatment with prism glasses, complicated surgery, and/or injection of muscle toxins.
None of the prior art treatments, however, provide ideal results. Specticals often do not correct the problem in all fields of gaze. Furthermore, specticals must be adjusted often. Surgery involves movement of a combination of the six extraocular muscles to different positions on the eye. Surgery of this nature is complex, often irreversible, and may not completely relieve the diplopia. Finally, muscle toxin injection involves Botulinum toxin. The effects of toxin injection are unpredictable, may cause further limitation of eye movement and must be repeated up to six times per year.
None of these prior art solutions reactivate the lateral rectus muscle 80, which would provide a true physiologic cure to diplopia. It would therefore be desirable to have a solution for diplopia that reactivates the lateral rectus muscle 80.
As is known to those skilled in the art, it is possible to externally stimulate the lateral rectus muscle in Rhesus monkeys. In general, neural stimulation of any body muscle is accomplished by neuronal impulses and occurs at the junction of the muscle and the nerve that stimulates that muscle. This junction is known as the neuromuscular junction. As is well known, neuronal impulses are of a single amplitude with a variable frequency. As the frequency of pulses to the muscle increases the contraction of the muscle increases in an exponential fashion. It is possible to measure the neuronal impulses to the extraocular muscles using microelectrodes. The prior art has demonstrated that is possible to stimulate a paralyzed muscle. The prior art, however, does not teach or suggest how to integrate the stimuli from other muscles in order to drive a paralyzed muscle.